1. Field of the Invention
The present invention relates to a lift truck which is used to load and unload a cargo.
2. Description of the Related Art
Conventionally, as a lift truck, there is widely used a lift truck which comprises a traveling motor for traveling a truck body of the lift truck, an electromagnetic brake for braking the rotation of the traveling motor, a brake operation device to be operated for actuation of the electromagnetic brake, and a brake controller for detecting the brake operation of the brake operation device to thereby actuate the electromagnetic brake.
In one type of conventional lift truck, as the above brake operation device, there is used a brake operation device which is exclusively designed for the brake operation. And, there is also known another type of lift truck in which there is disposed a lever type of steering device which can be operated swingable in the horizontal direction so as to control the traveling direction of the truck body, the steering device is used also as a brake operation device, and the electromagnetic brake is actuated when the brake controller detects that the brake operation device is situated at a given luffing angle.
In both types of conventional lift trucks, the electromagnetic brake can be controlled so as to be on or off and the brake force of the electromagnetic brake is designed such that it can cause the truck body, which is traveling with the maximum load and at the highest speed, to stop within a given brake distance.
However, in the structure in which the brake force of the electromagnetic brake is set at a given level in this manner, in case where an operator operates the brake operation device in a no-load condition where no cargo is present on the lift truck, or in a light-load condition where the cargo on the lift truck is light, the brake works more than necessary to thereby bring the truck body to a sudden stop. Especially, in case where the electromagnetic brake is actuated while the truck body is traveling in the no-load condition or in the light-load condition, the truck body is brought to a sudden stop.
In the light-load condition, this sudden stop can cause the cargo to collapse; or, in a lift truck of a type that an operator gets on the truck body and operate the same, the shock of the sudden stop causes the operator to lose his or her proper position and thus feel uncomfortable; or, there is also a fear that the operator, who has been out of balance due to the sudden stop or due to a reaction to the sudden stop, can unconsciously operate an operation lever by mistake.
Also, in case where the brake force of the electromagnetic brake is set at a given level in this manner, the feeling of the brake varies according to the traveling speeds of the truck body: that is, in the low-speed traveling condition, a sudden stop causes the operator to feel uncomfortable; and, on the other hand, in the high-speed traveling condition, not only the operator can doubt of the brake effect and thus can feel uneasy, but also the operator can be hasty or late in braking.